An electromagnetic flow meter is a device to measure a flow rate of fluid having electric conductivity. Electromagnetic flow meters include, a general type in which an electrode to detect a speed of flow is provided at an inner wall portion of a measurement pipe to flow fluid therein, and which is used for the measurement of liquid with an electric conductivity of not less than 3 μS/cm, in the state in which the electrode is in contact with the fluid, and a type called a capacitive type with a high input impedance in which an electrode is provided outside a wall between measurement pipes, and which can measure even an electric conductivity of pure water with an electric conductivity of not less than 0.01 μS/cm, in the state in which the electrode is not in contact with the fluid.
In such an electromagnetic flow meter, since there is not any operating portion at an inner wall of a measurement pipe to flow fluid therein, factors to raise the electric conductivity (to increase impurity content) are small, and since there is not any operating component, an electromagnetic flow meter is used for the flow rate measurement at the time of various cleanings, such as in cleaning devices in respective treatment processes in a semiconductor manufacturing process, and an adjusting device of chemicals concentration.
In a semiconductor wafer manufacturing process, for example, a pure water supplying device of an overflow system is used, and wafers are cleaned with pure water using a plurality of cleaning tanks. An electromagnetic flow meter is used for controlling a quantity of the pure water supplied to this cleaning tank (refer to Patent Document 1, for example).
In addition, in a residual chlorine measuring device to measure residual chlorine or residual concentration of other chemicals, concentration preparation with pure water is performed, and a flow meter is used for the flow rate control of the pure water (refer to Patent Document 2, for example).
In addition, also in a polishing device of a surface of a semiconductor wafer, a flow meter is used for controlling the pure water which is supplied for supplying abrading agent and for cleaning (refer to Patent Document 3, for example).
(Since the comparison with the following technical documents is indispensable, for setting problems so as to make clear the patentability of the present invention, the description of the contents and problematic points thereof will be described.)